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MD3002 Pathology > Bacterial and Viral Infections of the GI tract > Flashcards

Bacterial and Viral Infections of the GI tract Flashcards

(73 cards)

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1
Q

How can GI pathogens damage the body?

A
  • Local inflammation
  • Ulceration / perforation of mucosal epithelium
  • Disruption of normal gut microbiota
  • Pharmacological action of bacterial toxins
  • Invasion into blood or lymphatics
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2
Q

What can happen as a result of a ruptured / perforated ulcer?

A
  • May result in leaking of food and gastric juices to the peritoneal or abdominal cavities
  • Treatment requires surgery
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3
Q

What can happen to the villi as a resultof E. coli invasion?

A

Vilous atrophy

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4
Q

What are the stools like of someone affected by EPEC and cholera?

A

Watery

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5
Q

What bacterial infections can cause bloody stools?

A

Campylobacter and Shigella

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6
Q

Give some examples of bacterial diarrhoeal pathogens?

A
  • Vibrio cholerae
  • Escherichia coli
  • Campylobacter jejuni
  • Salmonella spp.
  • Shigella spp
  • Listeria monocytogenes
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7
Q

What are the features of V. cholerae?

A
  • Gram negative
  • Comma-shaped rod
  • Flagellated
  • Charecterised by epidemics and pandemics
  • Human-only pathogen
  • Flourishes in communities with no clean drinking water / sewage disposal
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8
Q

How can V. cholerae be desifered?

A

Based on O antigens

  • O1: Associated with early pandemics
  • Non-O1: 0139 associated with recent outbreaks
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9
Q

What are the 2 types of V. Cholerae vaccines?

A
  • Parenteral vaccine: low protective efficiency

- Oral vaccine: effective and suitable for travellers

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10
Q

How infective is V. Cholera and how does it infect humans?

A
  • Only infective in large doses
  • Many organisms killed in stomach
  • Colonisation of SI involving flagellar motion, mucinase, attachement to specific receptors
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11
Q

How do the V. cholerae cause diarrhoea?

A
  • Produces multicomponent toxin - CTx
  • Causes a massive increase of cAMP opening CFTR
  • Opening CFTR causes Cl- to move out of cell
  • Causes loss of fluid and electrolytes without damage to enterocytes
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12
Q

Describe the Cholera Toxin (CTx)

A
  • Oligomeric complex of 6 protein subunits
    1 copy of A subunit (enzymatic)
    5 copies of B subunit (receptor binding)
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13
Q

How much fluid is lost as a result of cholera infection and what does this result in if untreated?

A
  • 1 litre / hour
  • Electrolyte imbalance leading to dehydration, metabolic acidosis and hypokalemia
  • Hypovolemic shock
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14
Q

What is the mortality rate of cholera infection?

A
  • 40 - 60%

- <1% mortality if given fluid / electrolytes (ORT)

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15
Q

How would you describe stool from a patient with cholera?

A

Rice Water stool - completely fluid, no blood, mucous can be present

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16
Q

Describe the features of E. coli?

A
  • Gram negative
  • Bacilus
  • Member of normal GI microbiota
  • Can be resistant to acid
  • Some strains possess virulence factors enabing them to cause disease
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17
Q

What are the types of E. coli causing GI infections?

A
  • EPEC - enteropathogenic
  • ETEC - enterotoxigenic
  • VTEC/STEC - verocytotoxin-producing
  • EHEC - enterohaemorrhagic
  • EIEC - enteroinvasive
  • EAEC - enteroaggregative
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18
Q

What E. coli strain is known for causing travellers diarrhoea

A

ETEC (occurs in 20 - 50% of travellers)

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19
Q

What E. coli infection has sporadic cases and outbreaks of infection in under 5’s?

A

EPEC

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20
Q

What strain of E.coli is a food-borne infection in areas of poor hygiene?

A

EIEC

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21
Q

What bacteria creates a pedestal formation?

A

E. coli

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22
Q

What is an endotoxin?

A

It is actually part of the bacteria

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23
Q

What is an exotoxin?

A

Secreted by the bacteria

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24
Q

What does the heat-labile (LT) toxin produced by E. coli cause an increase in?

A

cAMP and secretion

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25
What does the heat-stable toxin (STa) produced by E. colicause an increase in?
cGMP and secretion
26
What bacteria is often found in undercooked chickens and the most common cause of diarrhoea in the UK?
Campylobacter jejuni
27
Desribe the features of C. jejuni?
- Gram negative - Helical bacillus - Large animal reservoir - Causes food-associated diarrhoea - Mucosal inflammation and fluid secretion
28
Describe the affect of C. jejuni infection on the SI from a histological point of view?
- Inflammation involves entire mucosa - Vilous atrophy - Necrotic debris in crypts - Thickening of basement membrane
29
What are the features of Salmonella spp?
- Gram negative | - Bacilli
30
How many serotypes of Salmonella spp are there?
> 2000 serotypes
31
How is Salmonella spp transmitted?
- Consumption of raw / undercooked meat, contaminated eggs and milk - Secondary spread can be human-human - Ingestion of large numbers of Salmonella to cause infection
32
What are some important Salmonella species?
- S. typhi - S. paratyphi - S. enteritidis
33
How does salmonella cause diarrhoea?
- Large numbers of salmonella bacteria ingested - Absorption to epithelial cells in terminal section of SI - Penetration of cells and migration to lamina propria - Multiplication in lymphoid follicles - Inflammation response mediates release of prostaglandins - Stimulation of cAMP - Release of fluid and electrolytes causing diarrhoea
34
What cac S. typhus and S. paratyphus cause?
- Enteric fevers: typhoid and paratyphoid - Systemic infections initiated in GI tract - Restricted to humans
35
What cells do S. typhi and paratyphi bacteria multiply and transport themsleves in?
Macrophages
36
How long can S. typhi stay in the stools for in patients with Typhoid fever?
Several weeks after recovery
37
How often often can S. typhi become a chronic infection in the body?
1-3% of the time, more common in women and the elderly
38
Name a notifiable disease
Typhoid fever (S. typhi)
39
What are the spots called that present on those with typhoid fever?
Rose spots
40
What are the 2 types of Typhoid vaccines?
``` - Oral; live attenuated booster needed after 5 years -Parenteral; capsular polysaccharide booster after 2 years - 50 - 80% effective - Recommended for travellers to endemic areas ```
41
What is the shape of Shigella spp?
- Bacillus
42
What does shigella spp. cause?
Shigellosis (bacillary dysentary) spread via human to human
43
What are the 4 species of Shigella spp?
- S. dysenteriae: most serious - S. flexneri: sever disease - S. boydii: severe disease - S. sonnei: mild infections
44
Describe the pathogenesis of Shigella infection?
- Attaches to mucosal epithelium of distal ileum and colon - Causes inflammation and ulceration - Rarely invasive - Produces Shiga toxin (STx) - Diarrhoe watery initially, later cacn contain blood and mucous - Usually self-limiting
45
Describe the shape of L. monocytogenes
Coccobaccillus
46
What does L. monocytogenes cause?
Listeriosis usually presents as meningitis
47
How many organisms are needed to cause listeriosis?
< 1000
48
What populations are at risk of Listeiosis?
- Pregnant | - Immunosuppressed individuals
49
What causes listeriosis?
- L. monocytogenes | - Can be present in pate, soft cheese, unpasteurised milk, humus
50
Name 3 viruses which can cause diarrhoea
- Rotavirus - Noravirus - Enteric adenovirus
51
Desribe the structure of rotavirus
- 'rota' - wheel | - 11 seperate segments of double-stranded RNA
52
Who is affected by rotavirus?
- Many mammals | - Most common in children < 2 years old
53
How is Rotavirus transmitted?
- Faeco-oral, but may also be faeco-respiratory - As few as 10 ingested particles can cause disease - It is a seasonal occurance
54
Describe the pathogenesis of rotavirus infection?
- Incubation period of 1-2 days - Replication of virus in SI epithelial cells at tips of villi - Results in villous atrophy - Damage caused to infected cells leaving immature cells with reduced absorptive capacity for sugar, water and electrolytes - Onset of vomitting, diarrhoea lasting 4 - 7 days
55
How many rotavirus particles are released per gram of faeces?
Up to 10^10 - 10^11
56
What virus causes the majority of sickness and diarrhoea outbreaks worldwide?
Norovirus
57
What percentage of adults have had norovirus at some point in their lives?
60%
58
How is norovirus transmitted?
- Human only pathogen - Transmission is faeco-oral, contaminated water / shellfish, fomites - < 100 virons can cause infection
59
What percentage of community-acquired diarrhoeas in young children are caused by enteric adenovirus?
10%
60
What is antibiotic-associated diarrhoea?
- Does not involve ingestion of pathogen or toxin | - Can arise from disruption of gut microbiota following antibiotic therapy
61
What bateria can overgrow in the gut as a result of tetracycline antibiotic therapy?
Allows colonisation by Staphylococcus aureus and candida sp.
62
What antibiotic suppresses the gut microbiota and allows Clostridium difficile to multiply?
Clindamycin
63
C. dificile is now associated with resistance to what antibiotic?
Vancomycin
64
How does C. difficle survive harsh conditions?
the production of spores - produces an enterotoxin and cytotoxin
65
Desribe the structure of Helicobacter pylori?
- Gram negative - Spiral - Flagellated - Microaerophilic - > 80% infected individuals are asymptomatic
66
What diseases can H pylori cause?
- Duodenal ulcers - Gastric ulcers - GORD - Non-ulcer dyspepsia
67
What are the key features of H pylori?
- Acid-inhibiting protein - survival in stomach - Urease - neutralisation of acid pH - Adhesins - ninding to gastric epithelium - Cytotoxin - damage to gastric epithelium - Flagellum - movement through gastric mucus layer
68
How is H pylori associated Gastritis treated?
``` - 1 week (7 days) triple therapy EITHER - PPI + clarithromycin + amoxycyillin OR - PPI + clarithromycin + Metronidazole ```
69
What is food poisoning?
Syndrome is restricted to diseases caused by toxins elaborated by contaminating bacteria in food before it is consumed
70
What are examples of toxins?
- Emetic toxins of Bacillus cereus - Enterotoxin of Staphylococcus aureus - Neurotoxin of Clostridium botulinum
71
What can Bacillus cereus be found in?
Rice
72
How does clostridium perfringens cause disease?
- Usually caused by type A strains from animal guts and soil - Contamination of raw meat products - Spores survives cooking and germination takes place - Multiplication in large intestine, production of spore and enterotoxin - Damage to intestinal epithelium - Diarrhoea
73
What is Oral Rehydration Therapy?
- Involves the replacements of fluids and electrolytes lost during diarrheal illnes - 90 - 95% of cases of acute diarrhoea can be successfully treated with an oral rehydration solution (ORS) - ORS increases the resorption of fluids and salts into the intestinal wall

MD3002 Pathology (19 decks)

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